The present invention relates to automatic replenisher systems for processors of photosensitive material. In particular, the present invention relates to an automatic calibration system which calibrates a sensor (such as a density sensor) of an automatic replenisher to eliminate inaccuracies in the sensor output caused by temperature variations, drift, and the like.
Photographic processors require replenishment of the processing fluids to compensate for the lowered chemical activity of the fluid which results from processing of the photosensitive film or paper. Replenishment systems originally were manually operated. The operator would visually inspect the film being processed and would manually operate the replenisher system as he deemed necessary. The accuracy of manual replenisher systems is obviously dependent upon the skill and experience of the operator.
In recent years, automatic replenishment systems have found increasing use. These systems typically utilize film density measurements and, in some cases, film speed measurements to control the operation of the replenishment system. Examples of automatic replenishment systems are shown in U.S. Pat. No. 4,057,818 by Gaskell and Charnley, and Ser. No. 4,104,670 by Charnley and Kumpula, both of which are assigned to the same assignee as the present application. Other examples of automatic replenisher systems may be found in U.S. Pat. Nos. 3,529,529 and by Shumacher; 3,559,555 by Street; U.S. Pat. No. 3,561,344 by Frutiger, et. al.; U.S. Pat. No. 3,696,728 by Hope; U.S. Pat. No. 3,752,052 by Hope, et. al.; U.S. Pat. No. 3,822,723 by Crowell, et. al.; U.S. Pat. No. 3,927,417 by Kinoshita, et. al.
The density sensors used in these automatic replenisher systems typically produce an analog density signal which is indicative of the density of the processed film. The density signal, however, can vary due to causes unrelated to the density of the film. For example, long term drift can cause a gradual change in the density signal totally unrelated to film density. In addition, the density sensor is often temperature sensitive so that in those systems in which the density sensor is positioned near a photographic dryer, the variations in the dryer temperature can cause erroneous fluctuations in the density signal.
In the past, some automatic replenisher systems have included a manual calibration adjustment for the density sensor. When the operator decides to calibrate the density sensor, he monitors or watches calibration outputs such as meters or lights and calibrates the density sensor by adjusting a dial until the desired calibration output is achieved. A manual calibration system, however, has several disadvantages. First, the accuracy of the calibration is operator dependent. Second, the calibration is time consuming for the operator. Third, the calibration is dependent upon the operator actually deciding to calibrate the density sensor. The accuracy of the system obviously depends on how often the operator decides to manually calibrate the density sensor.